linux-kernel - Re: [PATCH v3 2/4] platform/x86: dell

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Message-ID: <c213733e-e907-40cd-ab60-ec8fa0b15e4d@gmail.com>
Date: Fri, 30 May 2025 10:16:32 -0500
From: stuart hayes <stuart.w.hayes@...il.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: LKML <linux-kernel@...r.kernel.org>, Hans de Goede <hdegoede@...hat.com>,
 platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH v3 2/4] platform/x86: dell_rbu: Fix list usage

On 5/30/2025 2:54 AM, Ilpo Järvinen wrote:
> On Thu, 29 May 2025, Stuart Hayes wrote:
> 
>> Stop using an entire struct packet_data just for the embedded list_head,
>> and fix usage of that list_head.
>>
>> Fixes: d19f359fbdc6 ("platform/x86: dell_rbu: don't open code list_for_each_entry*()")
>> Signed-off-by: Stuart Hayes <stuart.w.hayes@...il.com>
> 
> Isn't this just refactor so Fixes tag for this commit is not warranted?
> 

No. The patch that this fixes had converted the driver to use 
list_for_each_entry*() to loop through the packet list instead of a 
while loop. But it passed (&packet_data_head.list)->next to 
list_for_each_entry*() instead of the list head itself.

That resulted in to issues. In the function that prints the packets, it 
would start with the wrong packet, and in the function that deletes the 
packets, it would get a null pointer dereference when it tried to zero 
out the data associated with the packet that held the actual list head.

>> ---
>>   drivers/platform/x86/dell/dell_rbu.c | 10 +++++-----
>>   1 file changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/platform/x86/dell/dell_rbu.c b/drivers/platform/x86/dell/dell_rbu.c
>> index 7b019fb72e86..c03d4d55fcc1 100644
>> --- a/drivers/platform/x86/dell/dell_rbu.c
>> +++ b/drivers/platform/x86/dell/dell_rbu.c
>> @@ -77,14 +77,14 @@ struct packet_data {
>>   	int ordernum;
>>   };
>>   
>> -static struct packet_data packet_data_head;
>> +static struct list_head packet_data_list;
>>   
>>   static struct platform_device *rbu_device;
>>   static int context;
>>   
>>   static void init_packet_head(void)
>>   {
>> -	INIT_LIST_HEAD(&packet_data_head.list);
>> +	INIT_LIST_HEAD(&packet_data_list);
>>   	rbu_data.packet_read_count = 0;
>>   	rbu_data.num_packets = 0;
>>   	rbu_data.packetsize = 0;
>> @@ -183,7 +183,7 @@ static int create_packet(void *data, size_t length) __must_hold(&rbu_data.lock)
>>   
>>   	/* initialize the newly created packet headers */
>>   	INIT_LIST_HEAD(&newpacket->list);
>> -	list_add_tail(&newpacket->list, &packet_data_head.list);
>> +	list_add_tail(&newpacket->list, &packet_data_list);
>>   
>>   	memcpy(newpacket->data, data, length);
>>   
>> @@ -292,7 +292,7 @@ static int packet_read_list(char *data, size_t * pread_length)
>>   	remaining_bytes = *pread_length;
>>   	bytes_read = rbu_data.packet_read_count;
>>   
>> -	list_for_each_entry(newpacket, (&packet_data_head.list)->next, list) {
>> +	list_for_each_entry(newpacket, &packet_data_list, list) {
>>   		bytes_copied = do_packet_read(pdest, newpacket,
>>   			remaining_bytes, bytes_read, &temp_count);
>>   		remaining_bytes -= bytes_copied;
>> @@ -315,7 +315,7 @@ static void packet_empty_list(void)
>>   {
>>   	struct packet_data *newpacket, *tmp;
>>   
>> -	list_for_each_entry_safe(newpacket, tmp, (&packet_data_head.list)->next, list) {
>> +	list_for_each_entry_safe(newpacket, tmp, &packet_data_list, list) {
>>   		list_del(&newpacket->list);
>>   
>>   		/*
>>
>